Thermometry

Linde has designed an oxygen generator in many respects similar to the Claude generator, but working without the expan sion engine, which is really only effective in connection with large plants.

Oxygen in Industry.

It is estimated that in the year 1926 there were in Europe alone 281 works producing eighty-one mil lion cubic feet of oxygen from liquid air. Germany took the lead with 8o works producing 3o millions of cubic feet. France followed with 37 works producing 20 millions, while in Britain there were 25 works, which produced nine millions, though the production was 25% below normal owing to the coal strike. The most impor tant use of the gas is in conjunction with acetylene, coal gas, or natural gas for cutting steel, and for welding steel, cast-iron, and other metals and alloys. It is almost universally used for cut ting metal plates and bars which are too heavy or too hard to shear, and it furnishes almost the only practicable method of shaping and cutting armour-plating. In cutting metal, the point at which the cut is to be started is heated in the oxyacetylene flame till the temperature is reached at which the metal burns. The acetylene is then shut off, and the jet of oxygen moved in the direction which the cut is to follow. The metal is removed in a stream of sparks, consisting of the molten oxide, leaving a clean cut through the plate. The process is applied to steel, but a skilled worker can cut cast-iron with an oxygen jet, making a rough cut such as may be allowable in breaking down large cast ings. Welding with the oxy-gas blowpipe is applied to all kinds of metals, the metal being heated along the line of the joint, which is filled in with the aid of a rod of the same metal, or of a suit able alloy, as in the process of soldering. Another important technical use of liquid oxygen is as a means of storing oxygen for use by pilots of aircraft when ascending to great heights, the weight of the container being a very small fraction of the weight of a steel cylinder required for the transport of the same weight of compressed oxygen. The oxygen for respiration is evaporated and the gas collected in a rubber bag is breathed through a respirator.

Liquid oxygen is used as an explosive by absorbing it by char coal, or other combustible material, contained in a paper cart ridge, and exploding the charge by fuse and detonator. Charcoal is used which absorbs upwards of three times its weight of liquid oxygen, so as to ensure complete combustion, according to the The heat evolved in exploding black powder and blasting gelatine is approximately 700 and 1,65o KC. respectively, and though the heat liberated is not a direct measure of the effectiveness of an explosive, it serves as an indication of it. Liquid air explosives have the particular advantage that they give rise to no noxious fumes, and misfires are not a source of danger.

The Rare Gases from Liquid Air.

The manufacture of argon has become important as furnishing the gas for filling elec tric glow lamps. Since argon boils at a temperature (--185.7) below that of oxygen the argon tends to concentrate in the liquid on the lower plates of the low pressure fractionating column. The

liquid can be drawn off and submitted to further fractional evapo ration. Neon and helium are also produced on a manufacturing scale by condensation and rectification of the most volatile frac tion of the liquid air.

As an example of the application of low temperatures to the separation of gases by liquefaction and fractional distillation we may take the investigations of Ramsay and Travers on the inac tive constituents of the atmosphere. By evaporation of liquid air a small residue of liquid was obtained which was found to con sist mainly of oxygen. On removal of oxygen a residue was ob tained which on spectroscopic examination was found to consist mainly of argon ; but which evidently contained some previously unknown gas. The density of this residue was slightly greater than that of argon. Larger quantities of the residue were obtained and the gas was then treated in the following manner :—It was intro duced into the reservoir A of the apparatus shown in fig. 25, and this communicated through a stopcock with the bulb C which was immersed in liquid air contained in a vacuum vessel, and through the stopcock D with a mercury pump. The bulb C was exhausted, the stopcock D was closed, and the gas from A was allowed to flow into C, in which it was condensed, either by increasing the pres sure in A, by raising the mercury reservoir connected with it, or by lowering the temperature of the liquid air by connecting the outlet from the vacuum vessel with an exhaust pump. This pro cedure was necessary since the gas consisted mainly of argon which boils at —185.7° C., while the temperature of liquid air consisting mainly of oxygen was about —183° C. When the whole of the gas was condensed it was allowed to evaporate, the gas passing back into A in six successive fractions; i.e., when a small quantity of gas had collected in A the stopcock was closed and this gas was transferred to a storage tube. Further quantities of gas were collected in the same manner, and finally the stopcock C was closed, the stopcock D was opened, the liquid was removed and the residue remaining in B passed into the mercury pump, which was arranged so that this quantity of gas could also be col lected. Numbering the fractions obtained two to seven, fraction two, the fraction collected first, contained the most volatile gas, and fraction seven the least volatile gas. Fraction two was dis carded; fraction three was then introduced into A and condensed in the bulb C. About two-thirds of it was then allowed to evapo rate back into A and the gas was transferred to a storage tube as fraction eight. Fraction four was then condensed with the residue in C, and again par tially evaporated, the most vola tile portion forming fraction nine. The same operation was re peated with fractions five, six and seven, and new fractions ten, i i and 12 were collected through A, a last fraction, 13, being taken into the pump and collected as before.